“He likes dirty things,” the source says. “He really gets off on one particular porno with a guy in a wheelchair. He’s attracted to things he can’t imagine happening to him.” Adding that Russell had a closet full of sex toys.

Plus the four other reasons why Russell bailed on the marriage:

Russell hated being alone: “Russell always needs someone there and that’s not Katy,” the source says. “She’s busier than he is.”

Katy’s hard partying lifestyle and friends really bothered him: “Russell can’t be in clubs because of his recovery and Katy didn’t want to give up the partying. She didn’t want to even compromise. That infuriated Russell.”

Russell wanted to start a family: “When he asked Katy about [having kids],” the source says. “Katy would just smile and says she was too busy.”

Russell wasn’t supportive of Katy’s career: “She had so many things going on this year and there were so many times he wasn’t there,” the source says. “He told her she wasn’t funny [when she hosted SNL] and he was totally uninterested [when he sat front row at her last concert]. He seemed annoyed he was there. I don’t think he sat through one whole song.”